Synthesis Of Chiral Wide-bandgap Fluorene-based Polymers And Properties Of Circularly Polarized Light

Due to the magneto-optical properties of circularly polarized light（CPL）,materials with CPL property have great potential in various applications such as 3D display,optical storage,optical encryption,optical detection,lasers and asymmetric synthesis.However,CPL is predominantly obtained through physical method which utilize polarizers and wave sheets,resulting in substantial loss of brightness and energy.Furthermore,the physical method requires relatively complex device structures.Consequently,researchers have directed their efforts towards chiral materials intrinsically emitting CPL,with the development of organic light-emitting diodes.CPL materials can be categorized into five groups,namely organic small molecules,polymers,supramolecular assemblies,metal complexes,and liquid crystal CPL materials.Among these materials,polymer CPL materials have gained significant attention due to their ease of synthesis and fabrication,easy processing,high thermal stability,and flexible ways to adjust their structure and properties.Fluorene-based polymers are one such polymer material that exhibit many exceptional properties,including deep-blue light emission,high fluorescence efficiency,multi-phase transition,high stability,easy chemical modification,and wide applications in organic light-emitting diodes and organic lasers.Accordingly,this paper focusses on the design and synthesis of fluorene-based polymers with chiral groups and investigates their physicochemical and CPL properties.In the first part,poly（9,9-diarylfluorene）PODPF-Chiral with chiral side chain was synthesized,and chiral alkyl chain-（S）-2-methylbutyl was introduced at the 4-position side group position of fluorene,thus polyfluorene PODPF-Chiral with chiral side chain containing chiral group was synthesized,which was found to have excellent thermal stability,spectral stability and deep-blue light by testing.The PODPF-Chiral exhibited CPL performance in drop-coated films,and further self-assembled into nanomicrosphere films by co-blended solvent method,the CPL performance was greatly amplified,and the asymmetry factor g_lum achieved a 50-fold expansion from-0.004 to-0.213in drop-coated films,realizing efficient CPL emission,indicating that the self-assembled microstructure is more favorable for chiral transmission and amplification of circularly polarized luminescence.In the second part,the chiral fluorene-based nanogrid polymer PODPFG-Chiral was synthesized,based on the extended lattice of diaryl fluorene skeleton and the introduction of chiral alkyl chain-（S）-2-methylbutyl on the carbazole nitrogen atom of the poly lattice skeleton,thus synthesizing the chiral poly lattice PODPFG-Chiral,which was found by testing to have excellent thermal stability,spectral stability and deep-blue luminescence properties.PODPFG-Chiral did not exhibit CPL in trichloromethane,tetrahydrofuran,toluene dilute solution and spin-coated films,while it exhibited CPL properties in drop-coated films with g_lum up to-3×10^-3,indicating that polygel has excellent potential in the field of CPL materials.In the third part,the chiral poly（spiro[fluorine-9,9’-xanthene]）PSFX-Chiral was synthesized by introducing a chiral alkyl chain-（S）-2-methylbutyl in the xanthene unit,thus synthesizing a chiral conjugated interrupted polymer,namely the chiral poly（spiro[fluorine-9,9’-xanthene]）PSFX-Chiral,which was found to have excellent thermal stability,spectral stability and blue-violet luminescence by testing.The chiral interrupted polymer,PSFX-Chiral,was tested for its thermal stability,spectral stability and blue-violet light emission.The CPL properties were tested,but no CPL emission was exhibited in both solution and thin film states.We speculate that this is due to the fact that the chirality is not effectively transferred to the polymer backbone due to its conjugated interrupted linkage and rigid structural units,and therefore no CPL can be induced,which indirectly proves the superior chiral transfer and circularly polarized luminescence of the diarylfluorene backbone and nanopolymer system.